(a) Field of the Invention
The present invention relates to a modular plug and, more particularly, to a modular plug capable of improving cross-talk characteristics of the higher-frequency signal components in the signal transmitted through the modular plug.
(b) Description of the Related Art
Modular plugs are generally attached onto both ends of modular cables connecting together a variety of information equipment such as telephone set, personal computer, modem and facsimile. The modular cable connecting together the information equipment such as a personal computer for communications includes a plurality of twisted-wire pairs, wherein a specified modular plug is connected to each end of the modular cable for the convenience of electrical connection and for adapting the request from the standardized equipment.
FIGS. 23 and 24 show a conventional modular plug connected to an end of a modular cable 11 in perspective views. FIG. 23 shows the modular plug 12 from the topside thereof mounting thereon pressure contact terminals 13, whereas FIG. 24 shows the modular plug 12 from the bottom side thereof mounting thereon a clip 14.
FIG. 25 shows the conventional modular plug 12 during connection to a modular cable 11 including a plurality of twisted-wire pairs 16. The front end portions 17 of the twisted wires of a twisted-wire pair 16 are unraveled, or released from one another, and the unraveled wires 17 are inserted into the housing 19 of the modular plug 12 in the direction of an arrow 18. Each tip of the unraveled wire 17 is fixed by a pressure contact terminal (terminal), which is not specifically shown in the drawing and pressed by a corresponding electrode of the modular jack.
Mere insertion of the wires 11 into the modular housing 19 and application of the pressure contact to the wires provide the structure of the connected modular plug shown in FIGS. 23 and 24. The modular plug 12 is used in combination with a modular jack as a connector by inserting the modular plug 12 into the opening of a modular jack. This combination of connector is widely used in the communication industry due to a low cost for the connection.
In a data network communication equipment, there is an ever request for a higher bit-rate communication and a problem of an increased terminal cross-talk, especially in a broadband communication. The term “terminal cross-talk” as used in this text means a cross-talk occurring in a connector nearest to the communication equipment, wherein the output signal of a transmitter in the equipment is mixed into the input signal of a receiver in the equipment. The terminal cross-talk results from a capacitive coupling between adjacent wires or between adjacent electrodes in the modular connector, degrading the signal quality in the communication.
For example, the twisted wires of a wire pair 16 in the modular cable 11 shown in FIG. 25 are unraveled from the twisting at the tip portion 17 of the wires to extend parallel to one another, thereby generating terminal cross-talk at the parallel running portions of the wires.
TIA/EIA-568 (TIA/EIA; The US Telecommunications Industries Association and Electronics Industries Association) issued by ANSI (American National Standards Institute) and ISO/IEC-11801 (ISO/IEC: International Organization for Standardization) prescribe standards of wire connection, which is vulnerable to an external electric disturbance and susceptible to the cross-talk.
FIG. 26 schematically shows an example of conventional connections of wires to a modular plug, wherein first to fourth wire pairs 161 to 164 are connected to first to eighth terminals 211 to 218 of a terminal board 13 of the modular plug. The wires of first wire pair 161 and fourth wire pair 164 are connected to the respective terminals in the order of arrangement of the wire pairs 161 and 164 and arrangement of the terminals 211, 212, 217 and 218. In this example, by setting the distance between the first wire pair 161 and the second wire pair 162 and the distance between the third wire pair 163 and fourth wire pair 164 larger than the distance between second wire pair 162 and the third wire pair 163, the cross-talk between the unraveled wires running parallel to one another after unraveling from the twisted state can be alleviated.
However, the connections of the wires to the terminals of the modular plug involve an intersection between one of the unraveled wires from the second wire pair 162 and unraveled wires from the third wire pair 163 due to the arrangement of the terminals 213, 214, 215 and 216 of the terminal board 13 The intersection between the unraveled wires incurs the problems of external disturbance and cross-talk therebetween. JP Patent Publication 2002-510854 of a PCT application, for example, describes a technique for reducing the influence by cross-talk in such a case (FIGS. 32 and 33 in the publication).
FIG. 27 shows the structure described in the patent publication, wherein a support block 31 depicted in a sectional view is disposed in the vicinity of the terminal board in the modular plug, the support block 31 having slots for passing therethrough and supporting the unraveled wires 321 to 328. These slots are arranged such that the wires 323 and 326 are disposed at a vertical distance D1 apart from the other wires, as viewed from the center-to-center distance. The larger distance between the unraveled wires 32 reduces the capacitive coupling between the wires 32 and thus the cross-talk therebetween.
In the structure described in the patent publication, however, there also remains portions of the unraveled wires of the wire pairs running parallel to one another outside the support block 3. The parallel running of the unraveled wires inevitably incurs the problem of the terminal cross-talk depending on the bit rate of the data communication.